Olivier: Consequences of Phytoplasma Infection on Canola Crop Production in the Canadian Prairies
Date: 2008
Term: n/a
Status: Completed
Researcher(s): C. Olivier and B. Galka, Agriculture and Agri-Food Canada, Saskatoon, SK
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: n/a
Project Summary
In Canada, Aster Yellows Disease (AY), caused by ‘Candidatus Phytoplasma asteris’ affects several economically important crops including canola. Until recently, the disease has been considered to be of little importance, however, in 2007 crop production losses were higher than estimated with the visual AY assessment. The objectives of this project were to use PCR tests to determine an accurate incidence of AY disease, and to estimate the percentage of seeds infected with AY and their viability. The results showed that AY phytoplasma are present in a large proportion of asymptomatic plants meaning that canola production losses will be higher than estimated from visual assessment of AY incidence. The presence of AY DNA in seeds and seedlings from infected seeds was observed.
In Canada, Aster Yellows Disease (AY), caused by ‘Candidatus Phytoplasma asteris’ affects several economically important crops including canola, both Brassica napus and B. rapa. Canola plants infected with AY phytoplasma show symptoms such as stunting, leaf yellowing or purpling, phyllody and formation of bladder-like siliques as well as normal-looking pods containing small misshapen seeds. Until recently, the disease has been considered to be of little importance, with overall incidence less than 1% in most fields.
Figure 1. Misshapen and normal crops in looking seeds harvested on an AY infected canola plant.In 2007, the percentage of canola plants showing symptoms ranged from traces to 12% depending on the location, with a Saskatchewan provincial average of 2%. However, in 2007 crop production losses were higher than estimated with the visual AY assessment. Seed productions were below average and high numbers of misshapen seeds were observed in harvested field seeds.
The objective of this research was to use PCR (Polymerase Chain Reaction) technology DNA tests 1) to determine an accurate incidence of AY disease in canola crop, 2) to estimate the percentage of seeds infected with AY phytoplasma and study their viability and 3) to determine if phytoplasma are present in seedlings grown from AY.
In August 2007, canola plants showing typical AY symptoms and canola plants showing no AY symptoms were collected in commercial fields of B. napus and B. rapa canola in Saskatchewan. DNA of AY phytoplasma was detected by PCR technology in every canola plant showing typical AY symptoms and in 10-30% of asymptomatic canola plants. AY phytoplasma DNA was found in leaf, stem and root tissues as well as in normal-looking and misshapen seeds of infected plants.
The presence of phytoplasma DNA in symptomless AY-infected plants means that the % of infected plants is greater than the % of plants showing AY symptoms. Based on these results, an estimated 25% and 32% of plants were infected by AY in fields showing 2% and 7% of plants with symptoms, respectively. Considering that AY infected plants produced 30-70% of misshapen seeds, seed production losses could be estimated at 0.6-1.5% for the field with a 2% AY incidence and 2 – 5% for the field with a 7% AY incidence.
AY phytoplasma DNA was also detected in seeds and seedlings growing out of seeds harvested on AY-infected canola plants, suggesting that phytoplasma are present in the seeds. PCR performed on plants grown out of infected seedlings became negative after the 4 leaf stage, suggesting that the phytoplasma do not remain viable as the plant grows.
Table 1. Average AY incidence in canola Saskatchewan, assessed by visual observations or PCR tests.
Scientific Publications
Olivier, Séguin-Swartz, Hegedus and Barasubiye. 2006. First report of Candidatus asteris phytoplasma subgroups AY 16SrI–A (strains WB and CHRY 16S) and 16SrI–B in Brassica rapa in Saskatchewan, Canada. Plant Disease, 90(6): p832.
Olivier, Murza, Galka, Hegedus, Barasubiye, Seguin-Swartz, Olfert, and Boudon-Padieu. 2006. Survey of Aster Yellows disease in canola crops in Saskatchewan, Canada, 2001-2005. Cruciferae Newsletter, 26: 40-42.
Olivier. 2007. Aster Yellows. In : Compendium of Brassica Diseases, Rimmer, R.SShattuck, V. And Buchwaldt, L. (Eds). The American Phytopathological Society Press, p 62-64.
Olivier, Galka, Rott, and Johnson. 2008. First report of ‘Molecular detection of ‘Candidatus Phytoplasma asteris’-related strains in seeds of Brassica napus in Saskatchewan, Canada. Cruciferae newsletter, 27: 22-23.
Olivier, Lowery, and Stobbs. 2009. Phytoplasma diseases and their relationships with insect and plant hosts in Canadian horticultural and field crops. The Can. Ent. 141: 425-462
Olivier, Seguin-Swartz and Galka. 2010. Detection of ’Candidatus Phytoplasma asteris’ in seed and seedling tissues of canola (Brassica napus and B. rapa). Canadian Journal of Plant pathology. 32: 298-305
Olivier, Séguin-Swartz, Galka and Olfert. 2011. Aster yellow in leafhoppers and field crops in Saskatchewan, Canada, 2001-2008. The Americas Journal of Plant Sciences and Biotechnology (in press).